Well bore conduit centering apparatus



July 1, 1958 M. B. CONRAD ET AL 2,841,226

WELL BORE CONDUIT CENTERING APPARATUS A TTOQNE YS' July 1, 1958 M. B. CONRAD ETAL WELL BoRE c'oNDuT CENTERING APPARATUS Filed Nov. 24. 1953 3 Sheets-Sheet 5 INVEN TOR. @WQ/227?? 29. Uwe/:dd

A WO2/VE YS United States Patent O 2,841,226 WELL BRE CDNDUET CENTERING APPARATUS Martin B. Conrad, Downey, and .lohn F. Muse, Whittier, Calif.; assignors to Baker Uil Tools, line., Los Angeles, Calif., a corporation of California Application lNovember 24, 1953, Serial No. 394,@33

13 Claims. (Cl. 166-213) The present invention relates to apparatus for centering stringsof wellcasing, and similar conduit strings, in well bores.

Itis desirable to secure-the substantial centering of a string of well casing in a well bore=to insure theAobtaining of a good cement job vthrough the proper placing of the cement slurry completely around the well casing. Some centering devices employ outwardly bowed springs mounted on the casing, which engagethe wall of the well bore, and thereby tend to hold the casing string approximately in a central position within the well bore. In order to be eifective, the bowed height of each spring should-be such that the spring bears upon the wall of a well bore and exerts suliicient centering force on the well casing to shift it toward acentered position.

When springs ofsuirlcient bowed height are used, Vthey are oftentimes diicult to start inthe surface casing at the top ofthe wellv bore, especially when there is comparatively small clearance between the surface casing and the casing onl which the centering springs are mounted. This is due to the force required to collapse the springs inwardly toward the casing on which they are mounted. Moreover, a` large inward deflection or collapse of the springs causes the outward force exerted by them against the surface casing to be high, resulting in high sliding friction between the surface casing and springs that might cause excessive Wear and possible spring breaking. in addition, thevlarge inward deilection of the springs can result in their permanent inward ilattening or deformation, rendering them incapable of centering the well casing when lowered in the open hole below the surface casing.

Accordingly, it is an object ofthe present invention to provide a casing centering apparatus capable of being easily started and moved through the surface casing, and in which the centering device can still effectively center the well casing on which it is mounted when disposed in open hole below the surface casing.

Another object of the invention is to provide acasing centering device embodying outwardly bowed springs that are initially disposed in a comparatively inward position and in which the bowed height and centering force of the springs can be increasedl after the apparatus has been started in the well bore.

A- further object of the invention is to provide casing centering apparatus embodying outwardly bowed springs disposed initially in a comparatively yretracted position, and which are automatically expanded outwardly after the device has been disposed in the well bore.

Yet another object of the invention is to provide -a casing centering device embodying centering elements disposed initially in a comparatively retracted position, and which are expanded outwardly by the hydrostatic pressure of iluid in the well bore in which the centering device has been disposed.

Still a further object of the invention is to provide a casing centering device embodying centering elements, such as outwardly bowed springs, which are expanded outwardly by iluid pressure in the wellV bore externally of the casing string on which the centering device is mounted.

Cil

This invention possesses many other advantages, and has other objects which may be made more clearly apparent from a consideration of several forms in which it may be embodied.l Such forms are shown in the drawings accompanyingand forming part of the present specification. These forms will now be described in detail, illustrating the general principles of the invention; but it is to be understood that such detailed description is not to be taken in a limiting sense, since the scope of the invention is best delined by the appendedclaims.

Referring to the drawings:

Figure 1 is a longitudinal section through one embodiment of the invention disposed in a well bore, with the spring centering elements arranged in a comparatively retracted position;

Fig. 2 is a view similar to Fig. l, parts being shown in side elevation, disclosing the spring elements expanded outwardly against the wall of the well bore;

Fig. 3 is an enlarged cross-section taken along the line 3 3 on Fig. 2;

Fig. 4 is an enlarged fragmentary longitudinal section disclosing the hydraulic actuating portion of the apparatus;

Fig. 5 is a longitudinal section through anotherV embodiment of the invention, with the springs in retracted position;

Fig. 6 is a view similar to Fig. 5, disclosing the springs in their outwardly expanded position against the wall of thewell bore.

In the specific forms of invention disclosed in the drawings, a plurality of circumferentially spaced centering elements, such as outwardly bowed springs, are arranged around a well casing that is to be lowered in the well bore, the springs initially occupying a cornparatively retracted position and capable of exerting a comparatively low centering force when engaged with the wall of an enclosure, such as a string of surface casing through which the well casing and centering apparatus isto be lowered. In view of the comparatively small force exerted by the centering springs, it is a cornparatively easy matter to lower a casing string through the surface casing in the well bore. However, after the casing string has been lowered a certain distance through the fluid in the well bore, the pressure of the lluid externally of the well casing is availed of to increase the centering action of the apparatus by causing the centering elements, such as outwardly bowed springs, to be expanded laterally outward into engagement with the wall of the confining well bore. More specifically, the hydrostatic pressure of the well bore fluid is Yavailed of to effect the outward expansion of the centering elements of the casing centering apparatus. Y

IIn the form of invention disclosed in Figs. l to 4, inclusive, a casing lcentering apparatus is mounted on a section of a conduit string, such Ias a well casing string A, which is to be moved through a well bore B. The casing centering apparatus includes a lower collar l0 surrounding the casing section A, to which the lower ends l1 of -circumferentially spaced, outwardly bowed springs 12 are secured, as through the use of welding material i3 that integrates the lower ends of the spring-s to the upper portion of the lower collar. The upper ends 14 of the springs `are received within the depending skirt portion 15 of an upper collar 16, such upper ends of the springs being slidable longitudinally within the collar and being stepped, engaging the lower, stepped end of a hydraulically operable sleeve or annular piston 17 which is slidable within the upper collar.

The upper collar 16 has an upper comparatively large diameter cylinder wall 18 and a smaller diameter cylinder wall 19 therebelow which ends-at an inwardly-directed shoulder20 in the upper collar capable of'functioning as a limit or stop, serving to determine the downward movement of the sleeve or piston within the upper collar, as explained hereinbelow. The annular piston 17 has an inner wall 21 of a diameter slightly greater than the diameter of the casing A on which the apparatus is mounted. However, the outer portion of the piston is constituted by la comparatively large head 22 slidable along the wall of the larger collar cylinder wall 1S. The piston also has a lower smaller diameter head 23 slidable along the smaller diameter cylinder wall 19. The larger head has a peripheral groove 24 therein to accommodate an elastic seal ring 25, such as a rubber O-ring, adapted to slidably and sealingly engage the larger cylinder wall 18. Similarly, the smaller head 23 has a peripheral ring groove 26 accommodating an elastic seal ring 27 such as a rubber O-ring, slidably and sealingly engaging the inner wall 19 of the smaller diameter cylinder. The upper seal 25 prevents the uid in the well bore from passing downwardly between the upper head 22 and upper cylinder wall 1S. Likewise, the lower seal 27 prevents fluid from passing upwardly between the lower head 23 and the smaller diameter cylinder wall 19. Thus, a confined cylinder space 28 is formed between the upper piston head 22 and cylinder -wall 18, on the one hand, and the lower piston head 23 and cylinder Wall 19, on the other hand7 into which the well bore uid cannot enter.

The upper ends 14 of the springs 12, as stated above, engage the lower end of the piston 17. Normally, the springs tend to occupy a comparatively retracted position with respect to the well casing A, such as disclosed in Fig. 1. When in such retracted position, the piston 17 occupies an upper position with its lower end `spaced above the collar stop shoulder 20. If desired, the piston may be retained in this position within the upper collar 16 by one or more shear screws 29 threaded transversely through the collar and received within a peripheral groove 3l) in the annular piston, preferably above the upper seal ring groove 24. In the absence of the shear screws 29, the upward movement of the piston 17 within the collar 16 would be limited by engagement of the upper end of the piston with a split stop ring 31 fitting within an internal groove 32 in the upper portion of the upper collar 16, and extending partially inwardly of the upper collar. This ring 31 tends inherently to expand in an outward direction, to retain itself within the collar groove 32.

The upper and lower collars 1t?, 16 are secured in longitudinally spaced relation with respect to each other by circumferentially spaced connecting bars 33, which are preferably disposed around the well casing A between the outwardly bowed springs 12. Thus, the upper ends 34 of the bars may be disposed within the upper collar skirt 15 and such ends may be permanently secured to this collar, as by plug welds 35. The lower ends 36 of the bars 33 abut the upper end of the lower collar 10, and may be integrated thereto, as by use of welding material 37. Inasmuch as the interconnecting bars 33 are comparatively rigid, they serve to secure the upper and lower collars 10, 16 a lixed distance apart. However, the upper ends 14 of the springs 12 are still free to move longitudinally relative to the upper collar 16.

The centering apparatus so far described could be slipped over the end of a casing section and secured thereto as by Welding the lower collar directly to the casing section. However, it is preferred not to weld the collar 10 to the casing section, but to provide a separate stop arrangement, now to be described. Thus, a stop ring 40 may be slidably disposed on the casing below the lower collar 10 from which it is spaced longitudinally by a. comparatively short distance. The lower spring collar 10 and stop collar 40 may be secured together by spot welding circumferentially spaced straps 41 to their external surfaces. A split stop ring 42 is mounted on the casing section A between the lower spring collar 10 and the stop collar 40, this split ring being fixedly secured to the casing section, as by the use of plug weld 43. Thus, the stop ring 42 is movable downwardly with the casing A to engage the stop collar 40, and, through the intervening metallic straps 41 and lower collar 10, will tend to pull the latter and the bowed springs 12 down through the well bore B. Similarly, the upper collar 16 is moved down through the well bore because of the interconnecting bars 33. In the event the casing A is moved in an upward direction, the stop collar 42 will engage the lower end of the lower spring collar 10, to shift the lower spring collar 10 and the upper collar 16 (connected thereto through the intervening bars 33) in an upward direction, carrying the outwardly bowed springs 12 and the remainder of the apparatus upwardly with the casing.

lt is to be noted that as the apparatus is lowered on the well casing A through the uid in the well bore B, the annular piston 17 is subjected to the pressure of the fluid externally of the well casing. Thus, the hydrostatic head of fluid is acting on the upper head end 22 of the annular piston over its annular area S, and tends to urge the piston 17 in a downward direction within the upper collar 16. At the same time, this hydrostatic pressure is acting in an upward direction over the lower head end 23 of the annular piston over its annular area R, tending to urge the piston in an upward direction. The fluid pressure in the well bore is ineffective to act on any portion of the piston 17 within the confined space 28, in view of the sealing rings 25, 27 engaging the large and small diameter cylinder walls 18, 19. Inasmuch as the area S is greater than the area R by the amount T, it is evident that the hydrostatic head of fluid will be effective to act over the differential area T to urge the piston 17 in a downward direction within the upper collar 16, or toward the lower collar 10. When the piston 17 can move in such direction toward the llower collar 10, it will shift the upper ends 14 of the springs 12 toward the lower ends 11 of the springs, in effect foreshortening the springs and causing their midportions 4S to be bowed outwardly to a greater extent. The extent of movement of the piston 17 within the upper collar 16 in a direction to expand the springs 12 outwardly is limited by engagement of the lower portion of the piston with the collar shoulder 20. Accordingly, a limit is placed on the extent of expansion or of the bowed height of the springs to avoid their overstressing and possible breakage. Y

Originally, the parts of the casing centering apparatus occupy the positions disclosed in Fig. l, in which the springs 12 are comparatively retracted on the well casing A, the piston 17 being disposed longitudinally away from the upper collar shoulder 20. The springs 12 may be retracted to the extent in which they actually will not engage the wall of the well bore, although this is a matter of selection. In any event, as the casing string A is lowered through the surface casing (not shown) near the top of the well bore, the springs 12, which are then bowed outwardly comparatively little, will offer a comparatively small resistance to downward movement of the casing A on which the centering apparatus is mounted through the surface casing. Such small resistance to longitudinal motion of the casing means that the bowed springs 12 are exerting comparatively little force against the wall of the surface casing. When the centering apparatus is disposed in the well bore below the surface casing, the bowed springs may not even engage the wall of the well bore B, in which event the centering apparatus may move slightly downward along the casing section A until the lower collar 10 engages the stop ring 42, which has been plug welded to the casing section.

As the centering apparatus is lowered through the fluid in the well bore B, the hydrostatic pressure. acting upon the annular piston or sleeve 17 increases. Longitudinal movementxof ithis1A piston toward thej lower: collar is resisted by the-.outwardlyfbowed springs i12I themselves.A Duringalowering of thefapparatuslin the fluid within the well bore the hydrostatic pressure gradually increases, forcing the'piston 17 down inthe collarv 16 and gradually increasing` the' bow ofthensprings until their mid portions 45 engagethe: wall of the well bore B. Continued movement ofthefannular piston 17 within the upper collar 16 and toward thenlowercollar `10r'will further foreshorten the springs. 12.and cause them to exert a greaterrforce upon Vthe wall of Vthe Well bore B, which reactively tends,` toi center` thexcasingstring A within the well bore. The extent offoutward. expansion of` the-v bowed springs is limited byiengagementof Vthe annular piston 17' with the upper collar' shou1der'20. The springs 12. will remain insuch outward'` position, inasmuchA as thelhydrostatic pressure of the fluid externally of the-well casingA is constantly-acting over the dilferential area Ton'rthe piston, tohold it in theposi'- tionrto which it has been-shifted' closer to the lower collar l0.

Once the springs 12 are engaging the wall'of the lwell bore B, downward movement of thecasing-stringA will cause the stop ring142 to engage the stop collary 40, to pull the lower collar 10in a downward direction through the intervening metal straps 41. In the event the springsl 12 encounter a restriction in the well bore, they will'be forced inwardly, the-*length of the springsincreasing, which increase in length is-permittedV by the lfact that the springs `will force the annular piston 17 away from the shoulder 20 to ltherequired extent against the hy draulic forceV provided by theV hydrostatic headV of ,iluid in the well bore around thefcasing. After the springs 12 have movedfbelow the restriction; they can again be expanded outwardly by the hydraulic' pressure movingthe piston-17 back to its original position in` engagement with the stop shoulder 20; v

In the event itis desired to prevent the springs 12 from `being expandedoutwardly from their initial retracted position Iuntil `the apparatus hasL been lowered to a predetermined depth in the well bore, the one or more shear screws 29'rnaybe used to secure the piston 17 in its initial position within the. upper collar 16. The shear screws will have the desired shear value, so as to disrupt at a predetermined pressure acting on the piston and corresponding to a predetermined depthwithin the well bore; As an example, the screws 29` maybe sheared by the hydrostatic head'acting jon'the piston 17 over the area T at a depth of 2000feet in the well bore. Accordingly, the springs will remain inV their initialV comparatively retracted position until the shearing depth of the screws 29 has been reached, whereupon the screws will be sheared, which then allows the hydrostatic head of iluid to shift the piston 17 withinthe upper' collar-16 toward the lower collarelt) and eiect the outward expansion ofthe springs 12' into iirm centering engagement with the wall of the well boreB.

The embodiment of invention disclosed in Figs. S and 6 operates in the same general'fashion as the one just described.4 However, the structure is specifically diierent. Thus, upper and lower longitudinally spaced spring collars 6d, 6i' are slidably mounted on a casing section A forming part of a casing string extending tothe top of the well bore. Circuinferentially spaced outwardly'bowed springs 62. have their upper and lower ends suitably secured, as by` welding, tothe upper and lower collars, respectively. The springs 62 normally tend to assume a comparatively retracted position, in whichtheir outwardly bowed height is substantially less than that finally desired. 'Y

Inner and outer hydraulically actuatable members6i,

65 are connected to the upper and lowercollars 60,61.V

Thusone of these members 65, such as therouter member, is disposed r at: an, intermediate v position along, the springs 62,-its upperendbeing secured, as by welding, to:,circum.

ferentially spaced connecting bars 66, the upper ends' of which are welded to the lower end of the upper collar 60.l The inner member 66 is slidable within the outer member 65, its lower en-d 'being connected, as by welding, to the upper ends of circumferentially spaced connecting bars 67, the lower ends of which are, in turn, suitably secured, as by welding, to the'upper end of the lower spring collar 61.

The inner hydraulic member 64 is in t-he Aform of a sleeve slidable on the casing section A and having a lower head portion 68 of a particular external diameter, above which a skirt portion 69 extends that has an external diameter smallerv than the external -diameter of the head 68. lThe outer hydraulic mem-ber has an upper head portion 7) slidable along the periphery of the skirt 69 and also a depending skirt portion 71 slidable along the head 68. In other words, the internal diameter of the upper head 70 correspondsto the external diameter of the skirt 69, and is less than the internal diameter of the skirt 71 which corresponds to the external diameter of the lowerhead 68.

A seal ring 72 is contained within a peripheral groove 73 in the lower head V68, slidably sealing against the inner wall of the skirt 71; whereas a seal ring 74 is also disposed within an internal groove 75 in the upper head 7), slidably and sealingly engaging the exterior of the skirt 69. Thusythe upper seal ring 74 engages the skirt 69 to prevent fluid from passing therebetween and into a space '76 formed between the heads and skirts 6E-7l. Similarly, the lower seal ring 72 prevents uid from passing upwardly between the skirt 7l and the lower head 68 into this space 76.V Therseal rings 74, 72 jointly prevent fluid from entering the space 76, in effect, constituting it as -a conned space into which wel-l bore uid cannot enter, and which will contain air initially at atmospheric pressure.`

The springs 62 normally tend to assume their comparatively retracted shape, such as shown in Fig. 5, in which position the heads 68, '7d are spaced from one another. However, when the hydrostatic 'head of fluid in the well bore is allowed to act on the heads, it will move them toward each other, correspondingly moving the upper and lower spring collars 69, 61 toward each other, to-

fores'horten the over-all length of the springs 62 and cause their intermediate portions 77 to be expanded outwardly into engagement with the wall of the well bore B. This actionof the hydrostatic head will occur on both the inner and the outer hydraulic members 64, 65. The

pressure of the Huid externally of the well casing is act ing in a downward direction over the annular area of` tiuid pressure is acting and tending to shift the outer hy- Similarly,

ldraulic member 65 in a downward direction. the hydrostatic head of uid in the well bore is acting over the annular area of the skirt 69 of the inner member `64, to urge the'inner member in a downward direction,

and over the annular area of the inner member head 63,.

tending to urge the inner member 64 in an upward direction. `Since the external diameter of the head 68 is greater than the external diameter of the skirt 69, the hydrostatic head of uid is acting over the differential cross-sectional area between the lhead 63 and the skirt 69,. tending to urge the inner member V6d in an upward direc-- tion. Accordingly, the hydrostatic head of fluid is urging the outer member 65 in a downward direction and the inner member 64H11 an upward direction, which will move the upper and lower spring collars 60, 61 toward each other, as limited by engagement of the heads 68, 70 with eachother to expand the springs 62 outwardly to a predetermined maximum extent.

A particular arrangement is disclosed for causing they casingwstring A tovmove the centering apparatus shownr in Figs. and 6 longitudinally in the well bore B. Thus, an upper ring 78 is spaced above the upper spring collar 60, being connected to the latter by means of the intervening circumferentially spaced metallic straps 79 that are spot welded, or otherwise suitably secured, to the exteriors of the upper ring and the upper spring collar. A stop ring 80, that has a longitudinal length less than the distance between the upper stop ring 78 and the upper collar 60 is plug welded, or otherwise suitably secured, to the casing section A. A lower ring 81 is slidably mounted on the casing A below the lower spring collar 61, being secured to the latter by intervening circumferentially spaced metal-lic straps 82 suitably secured to the lower spring collar 61 and lower stop ring 81, as by spot welding. A lower ring 83 is spot welded, or otherwise secured, to the casing section A between the lower spring collar 61 and the lower ring 83, the ring 83 having a longitudinal length substantially less than the distance between the lower ring 81 and lower spring collar 61.

If desired, the inner and outer hydraulically actuatable members 64, 65 may be secured to each other initially by one or more shear screws 85 to determine the depth in the well bore at which spring expansion will commence. However, the use of the shear screws is not necessary unless, for some reason, it is desired to prevent outward spring expansion until the centering apparatus has been lowered to a particular depth in the well bore.

The apparatus is mounted on a casing section, with the parts occupying the relative position shown in Fig. 5, the springs 62 being comparatively retracted with respect to the well casing A. They may be retracted sufficiently so as not to engage the wall of the well bore B when lowered therewithin, particularly near the top of the well bore. In view of the comparatively retracted position of the springs 62, they can be moved through surface casing with little dithculty. As the casing string A and the apparatus are lowered through the fluid in the well bore, the hydrostatic head of fluid is acting upon the differential areas of the inner an-d outer members 64, 65, urging .them toward each other until the resistance offered by the springs 62 to outward expansion is overcome, whereupon `the heads 68, 70 of the inner and outer members 64, 65 will be moved toward each other to correspondingly shift the lower and upper collars 61, 60 toward each other, the shifting occurring progressively, or gradually, as the apparatus is lowered through the fluid in the Well bore until the springs 62 are expanded to their fullest extent into engagement with the wall of the well bore B, as determined by contacting of the inner and outer heads 68, 7i? with one another (see Fig. 6).

In view of the resistance offered by the springs 62 to longitudinal movement of the apparatus in the well bore after engaging the wall of the latter, downward movement of the casing A will cause the lower stop ring 83 to engage the lower ring 81 and will pull the springs 62 down through the well bore. If a restriction in the well bore is encountered, the springs 62 will be urged inwardly, shifting the upper spring collar 69 inan upward direction and moving the hydraulic heads 68, 70 away from each other. Such upward movement of the upper collar 60 is permitted since, at this time, the upper strip ring 80 is spaced upwardly away from the upper co ar.

After the restriction has been passed', the springs 62 will again be urged outwardly by the hydraulic pressure acting on the upper and lower heads 70, 68, to the extent determined by engagement of the latter with each other. In the event that the casing string A is moved in an upward direction, the upper stop ring 80 will engage the upper ring 78, to again pull the springs 62 along the wall of the well bore. If a restriction is encountered, the springs 62 will be shifted inwardly, which will cause the lower collar 61 to be moved downwardly along the casing, pulling the inner hydraulic member 64 downwardly with respect to the outer hydraulic member 65.

8 After the restriction has been passed, then the hydrostatic head of fluid is again eiective to shift the heads 68, 70 back into engagement with each other to again expand the springs 62 to their predetermined maximum extent.

As was described in connection with the other form of the invention, if the shear screw is used, then outward expansion of the springs 62 will not occur until the apparatus has been lowered to a predetermined depth in the well bore uid corresponding to the shear value of the screws. When they are disrupted, the hydraulic head of fluid is allowed to move the heads 68, 70 toward each other and expand the springs 62 outwardly against the Wall of the well bore B.

It is, accordingly, apparent that apparatus has been provided which can be started easily in surface casing and moved therethrough, with the sliding friction minimized to a considerable extent. Despite this fact, the outwardly bowed springs are expanded outwardly to increase their bowed heights substantially, which will cause the springs to exert a substantial centering force on the casing string, tending to shift it and maintain it in a substantially centered position within the well bore.

The inventors claim:

1. In apparatus for centering conduit strings in well bores: a plurality of laterally expandible circumferentially spaced members adapted to extend longitudinally along and around the exterior of the conduit string; first means retaining the lower portions of said members in juxtaposition to the conduit string and preventing outward movement of said lower portions; second means retaining the upper portions of said members in juxtaposition to the conduit string and preventing outward movement of said upper portions; and hydraulically operable means connected to said rst and second means and responsive to the pressure of uid in the well bore externally of the conduit string for forcing and shifting said first and second means relatively toward each other and thereby expand said members laterally outward.

, 2. In apparatus for centering conduit strings in well bores: a plurality of laterally expandible circumferentially spaced members Vadapted to extend longitudinally along and around the exterior of the conduit string; first means retaining the lower portions of said members in juxtaposition to the conduit string and preventing outward movement of said lower portions; second means retaining the `upper portions of said members in juxtaposition to the conduit string and preventing outward movement of said upper portions; and hydraulically operable means connected to said first and second means and responsive to the pressure of fluid in the well bore externally of the conduit string for forcing and shifting said rst and second means longitudinally with respect to each other and thereby shift part of said members laterally of the conduit string.

3. In apparatus for centering conduit strings in well bores: a plurality of laterally expandible circumferentially spaced members adapted to extend longitudinally along and around the exterior of the conduit string; first means retaining the lower portions of said members in juxtaposition to the conduit string and preventing outward movement of said lower portions; second means retaining the upper portions of said members in juxtaposition to the conduit string and preventing outward movement of said upper portions; and hydraulically operable means connected to said rst and second means and responsive to fluid pressure in the well bore for forcing and shifting said first and second means relatively toward each other forcing and expanding said members laterally outward.

4. In apparatus for centering conduit strings in well bores.: a plurality of laterally expandible' circumferentially spaced members adapted to extend longitudinally along and around the exterior of the conduit string; first means retaining the llower portions of said members in juxtaposition -to the conduit string and preventing outward movement of ysajigl lower portions; second means retaining the upper portions of said members in juxtaposition to the conduit string and preventing outward movement of said upper portions; and hydraulically operable means connected to said iirst and second means and responsive to the pressure of fluid in the well bore for forcing and shifting said first and second means longitudinally with respect to each other and thereby shift part of said members laterally of the conduit string.

5. in apparatus for centering conduit strings in well bores: a plurality of circumferentially spaced outwardly bowed springs adapted to be longitud ally disposed around the exterior of the conduit string; rst means retaining the lower portions offsaid springs in juxtaposition to the conduit string and preventing outward movement of said lower portions; second means retaining the upper portions of said springs in juxtaposition to the conduit string and preventing outward movement of said upper portions; and hydraulically operable means responsive to iiuid pressure in the well bore for forcing and shifting one of said portions of said springs longitudinally toward the other of said portions of said springs and thereby expand the intermediate portions of said springs laterally outward.

6. ln apparatus for centering conduit strings in well bores: a plurality of circumferentially spaced outwardly bowed leaf springs adapted to be longitudinally disposed around the exterior of the conduit string; first means retaining the lower portions of said springs in juxtaposition to the conduit string and preventing outward movement of said lower portions; second means retaining the upper portions of said springs in juxtaposition to the conduit string and preventing outward movement of said upper portions; and hydraulically operable means responsive to the tiuid pressure in the well bore externally of the conduit string for forcing and shifting one of said portions of said springs longitudinally toward the other of said portions of said springs and thereby expand the intermediate portions of said leaf springs laterally outward.

7. In apparatus for centering conduit strings in well bores: upper and lower longitudinally spaced collars adapted to bedisposed on the exterior of the conduit string; a plurality of laterally expandible circumferentially spaced members adapted to extend longitudinally along and around the conduit string between said collars and having their upper and lower portions retained in juxtaposition to the conduit string by said upper and lower collars, respectively; and hydraulically operable means connected to said collars and responsive to the pressure of fluid in the well bore for forcing and shifting said collars relatively toward each other and thereby expand the intermediate portions of said members laterally outward.

8. In apparatus for centering conduit strings in well bores: upper and lower longitudinally spaced collars adapted to be disposed on the exterior of the conduit string; a plurality of laterally expandible circumferentially spaced members adapted to extend longitudinally along and around the conduit string between said collars and having their upper and lower portions retained in juxtaposition to the conduit string by said upper and lower collars, respectively; and hydraulically operable means connected to said collars and responsive to the pressure of fluid in the well bore externally of the conduit string for forcing and shifting said collars relatively toward each other and thereby expand the intermediate portions of said members laterally outward.

9. In apparatus for centering conduit strings in well bores: upper and lower longitudinally spaced collars adapted to be disposed on the exterior of the conduit string; a plurality of longitudinally extending laterally expandible circumferentially spaced leaf springs between said collars and having their upper and lower portions retained in juxtaposition to the conduit string by said upper and lower collars, respectively; and hydraulically 10 operable means responsive to the pressure of fluid in the well bore for forcing and shifting one of said portions of said springs longitudinally toward the other of said portions of said springs and thereby expand the intermediate portions of said leaf springs laterally outward.

10. In apparatus for centering conduit strings in well bores as defined in claim 9; wherein said hydraulically operable means comprises a first member operatively associated with one end portion of said springs and slidably sealed against a companion member to provide a confined space therebetween into which well bore uid cannot enter, whereby said rst member has oppositely facing transverse surfaces subject to the hydrostatic head of fluid in the well bore externally of the conduit string, the transverse surface of said first member facing toward the opposite end portion of said springs having a lesser area subject to such hydrostatic head of iiuid than the other transverse surface, whereby said first member is urged by the hydrostatic head of iiuid toward the opposite end portions of said springs to correspondingly move said one end portion of said springs toward the opposite end portion of said springs to bow the intermediate portions of said springs laterally outward.

11. In apparatus for centering conduit strings in well bores as deiined in claim 9; wherein said hydraulically operable means comprises an annular member slidable in and sealingly engaging one of said collars and engaging an end portion of said springs, said member and said one of said collars providing a confined space therebetween into which well bore fluid cannot enter whereby said member has a transverse surface facing said end portion of said springs of lesser area than an oppositely facing transverse surface to provide a transverse differential area subject to the hydrostatic head of fluid in the well bore externally of the conduit string tending to shift said annular member and end portion of said springs engaged thereby toward the other end portion of said springs to expand the intermediate portions of said springs laterally outward.

12. In apparatus for centering conduit strings in well bores as defined in claim 9; wherein said hydraulically operable means includes an annular member in one of said collars and engaging an end portion of said springs, said member having a first head slidably and sealingly engaging said one collar and a second head between said rst head and said end portion of said springs slidably and sealingly engaging said one collar, whereby fluid in the well bore cannot enter the region between said one collar and annular member located between said heads; the outside diameter of said first head being greater than the outside diameter of said second head.

13. In apparatus for centering conduit strings in well bores as defined in claim 9; wherein said hydraulically operable means comprises an outer annular member connected to one of said collars, an inner annular member connected to the other of said collars, said outer annular member having a head portion slidably and sealingly engaging a skirt portion of said inner annular member, said outer annular member also having a skirt portion slidably and sealingly engaging a head portion of said inner annular member, the outside diameter of said inner annular member head portion being greater than the outside diameter of said inner member skirt portion, said outer and inner annular members defining a confined space therebetween into which well bore uid cannot enter.

References Cited in the file of this patent UNITED STATES PATENTS 2,311,768 McCray Feb. 23, 1943 2,319,236 Isaacks et al. AMay 18, 1943 2,344,120 Baker Mar. 14, 1944 2,654,435 Oliver Oct. 6, 1953 2,712,920 Cullen et al July 12, 1955 

